1. Field of the invention
The present invention relates to an anti-skid (lock) control unit for vehicles.
2. Prior Art
There is known a prior art anti-skid control unit in which a single brake fluid passage is coupled to a wheel cylinder through which operation fluid (brake fluid) is supplied or discharged. Whereupon, in such a wheel cylinder, not only a braking operation or releasing operation of a brake unit is performed by depressing or releasing the brake pedal using the single brake fluid passage but also an operation involved in an anti-skid control is performed, namely, each operation for increasing, keeping or reducing fluid pressure is performed by using single brake fluid passage. Accordingly, a directional control valve is interposed on the brake fluid passage so as to be switched to a pressure increasing position, pressure keeping position, or a pressure reducing position.
However, since the directional control valve comprising an electromagnetic valve is needed to be controlled so as to be switched to the aforementioned three positions in the prior art anti-skid control unit, there arise problems in that the structure is complex and the control operation is delayed. For example, when the directional control valve is switched from the pressure increasing position to the pressure reducing position, the brake fluid passage is allowed to pass through the pressure keeping position, which takes time.